Saturn Approach

Three Voyager 2 images, taken through ultraviolet, violet and green filters, were combined to make this photograph.› Larger image

The Voyager 1 and 2 Saturn encounters occurred nine months apart,
in November 1980 and August 1981. Voyager 1 is leaving the
solar system. Voyager 2 completed its encounter with Uranus
in January 1986 and with Neptune in August 1989, and is
now also en route out of the solar system.

The two Saturn encounters increased our knowledge and altered
our understanding of Saturn. The extended, close-range observations
provided high-resolution data far different from the picture
assembled during centuries of Earth-based studies.

Here is a summary of scientific findings by the two Voyagers
at Saturn: SATURN Saturn's atmosphere is almost entirely
hydrogen and helium. Voyager 1 found that about 7 percent
of the volume of Saturn's upper atmosphere is helium (compared
with 11 percent of Jupiter's atmosphere), while almost all
the rest is hydrogen. Since Saturn's internal helium abundance
was expected to be the same as Jupiter's and the Sun's,
the lower abundance of helium in the upper atmosphere may
imply that the heavier helium may be slowly sinking through
Saturn's hydrogen; that might explain the excess heat that
Saturn radiates over energy it receives from the Sun. (Saturn
is the only planet less dense than water. In the unlikely
event that a lake could be found large enough, Saturn would
float in it.)

Subdued contrasts and color differences on Saturn could be a result
of more horizontal mixing or less production of localized
colors than in Jupiter's atmosphere. While Voyager 1 saw
few markings, Voyager 2's more sensitive cameras saw many:
Long-lived ovals, tilted features in east-west shear zones,
and others similar to, but generally smaller than, on Jupiter.

Winds blow at high speeds in Saturn. Near the equator, the Voyagers
measured winds about 500 meters a second (1,100 miles an
hour). The wind blows mostly in an easterly direction. Strongest
winds are found near the equator, and velocity falls off
uniformly at higher latitudes. At latitudes greater than
35 degrees, winds alternate east and west as latitude increases.
Marked dominance of eastward jet streams indicates that
winds are not confined to the cloud layer, but must extend
inward at least 2,000 kilometers (1,200 miles). Furthermore,
measurements by Voyager 2 showing a striking north-south
symmetry that leads some scientists to suggest the winds
may extend from north to south through the interior of the
planet.

While Voyager 2 was behind Saturn, its radio beam penetrated the
upper atmosphere, and measured temperature and density.
Minimum temperatures of 82 Kelvins (-312 degrees Fahrenheit)
were found at the 70-millibar level (surface pressure on
Earth is 1,000 millibars). The temperature increased to
143 Kelvins (-202 degrees Fahrenheit) at the deepest levels
probed - - about 1,200 millibars. Near the north pole temperatures
were about 10 degrees Celsius (18 degrees Fahrenheit) colder
at 100 millibars than at mid-latitudes. The difference may
be seasonal.

The Voyagers found aurora-like ultraviolet emissions of hydrogen
at mid-latitudes in the atmosphere, and auroras at polar
latitudes (above 65 degrees). The high-level auroral activity
may lead to formation of complex hydrocarbon molecules that
are carried toward the equator. The mid-latitude auroras,
which occur only in sunlit regions, remain a puzzle, since
bombardment by electrons and ions, known to cause auroras
on Earth, occurs primarily at high latitudes.

Both Voyagers measured the rotation of Saturn (the length of
a day) at 10 hours, 39 minutes, 24 seconds.